I'm still running basically the same system (NVidia 780l, E6750 OC'd to 3.2 Ghz, 4 Gb Kingston HyperX DDR2800, NVidia GTX9800+) and have no problems with AH outside of smooth shadows.
I've had a copy of Win 7 sitting here since August that I haven't installed yet as I was hoping my brother would return my NASCAR Racing disc before I did but alas I haven't seen it yet. I expect no problems with the upgrade but the longer I wait the more likely I'll upgrade my Mobo, CPU, CPU cooler, RAM and GPU before I get to it. In the meantime I'm still running XP Pro with no issues although I probably need to find a browser other than IE which XP supported versions of struggle with some of the newer web site code.
BTW, I bought a new laptop recently (MSI - Intel Core I5 4210 2.6 Ghz, 8 Gb RAM, NVidia GTX 820M 2 Gb, Win 8.1) for $700. While I haven't played AH on it yet I did install it and it installed with all graphics maxed by default and seems to run smoothly looking around from the tower. Pricing new guts for my old system and adding an SSD comes in just under $1000 (reusing case, PSU, HD's, Optical drives, keyboard, mouse, monitor and speakers).
After all these years I've recently had some positive movement in my income and work situation and finally have a little extra money to do a few things but I still have to be careful.